The present invention relates to wireless digital communication systems. More particularly, the present invention relates to a method and apparatus for convolution of spreading code, scrambling code and channel response within a wireless TD-CDMA communication receiver to calculate system transmission matrix coefficients.
During communications in a TD-CDMA system such as specified by the Third Generation Partnership Project (3GPP), each signal burst between a base station and a user equipment (UE) is transmitted and received along a frame structure that is broken into time slots. FIG. 1 shows the structure of a communication burst time slot comprising a predetermined midamble, specifically assigned by a base station to a UE for channel estimation purposes, located between two data symbol bursts. The midamble information is characterized by a number of chips, where TC represents the chip period and Lm is the midamble length. The midamble chips are transformed by a filter process in the receiver into a channel response consisting of real and imaginary components. Because a TD-CDMA system allows several UEs to be assigned to the same time slot, each has a unique spreading code and spreading factor tagged to it to distinguish one UE's midamble channel representation from another. Scrambling codes are attached to a signal to distinguish one base station from another, thereby preventing inter-base station interference, which potentially occurs when a UE is in the range of two nearby base stations.
As a wireless transmission travels through the air between a transmitter and a receiver, signal reflections and external noise effects create a received signal that is different from its original state. Therefore, within the communication system, it is useful to develop a representation of the known system transmission characteristics unique to the particular base station and UE. In 3GPP systems, a system transmission matrix A of coefficient values, and/or its complex conjugate transpose AH, is used for this purpose. Applying the received signal to the system transmission matrix coefficients is a way to extract the original signal data from the externally altered signal that was received.